AEArbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre of the Russian Academy of Sciences, Arbuzov str 8, 420088 Kazan, Russia.
Spectrochim Acta A Mol Biomol Spectrosc. 2010 Feb;75(2):872-9. doi: 10.1016/j.saa.2009.12.022. Epub 2009 Dec 16.
It is demonstrated that dissolution of aminothiacalix[4]arene in chloroform results in transformation of 1,3-alternate conformation, adopted in single-crystal and bulk polycrystalline solids, to the pinched-cone form. This conformer is stabilised by the intramolecular hydrogen bonds of two distal amino-groups acting as H-donors with another two amino moieties that appear as H-acceptors. The H-bonds cause quite small (ca. 10-20 cm(-1)) red shift of the IR bands of the NH(2) stretching vibrations, which suggests rather weak NHcdots, three dots, centeredN hydrogen bonding. This latter is sufficient to stabilize the pinched-cone conformation in the chloroform solution, but the energy gap between the pinched-cone and other conformations is small, and solid-state intermolecular forces easily overcome it, leading to realisation of the 1,3-alternate conformer. The comparison of the DFT computed and experimental vibrational and NMR spectra demonstrates good quality of present quantum-chemical computations, allows complete interpretation of the spectra and reveals simple IR and NMR spectroscopic markers of the conformers of aminothiacalix[4]arenes.
研究表明，氨基硫杂杯[4]芳烃在氯仿中的溶解导致其构象从单晶和多晶固体中所采用的 1,3-交替构象转变为夹挤锥形构象。这种构象通过两个远端氨基作为 H 供体与另外两个氨基部分之间的分子内氢键稳定，后者表现为 H 受体。氢键导致 NH（伸展振动的 IR 带发生相当小的（约 10-20 cm（-1））红移，这表明 NH······，三个点，以 N 为中心的氢键相当弱。后者足以在氯仿溶液中稳定夹挤锥形构象，但夹挤锥形构象与其他构象之间的能隙较小，固态分子间力很容易克服它，导致 1,3-交替构象的实现。DFT 计算和实验振动和 NMR 谱的比较表明，目前量子化学计算具有良好的质量，允许对光谱进行完整的解释，并揭示了氨基硫杂杯[4]芳烃构象的简单 IR 和 NMR 光谱标记。
